This application is based on Japanese Patent Applications No. 2001-55931 filed on Feb. 28, 2001, and No. 2001-389024 filed on Dec. 21, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a control system for an internal combustion engine.
2. Description of Related Art
In recent years, the regulations against the exhaust gas of a Diesel engine have been more and more strict to enhance the necessities for highly precise EGR controls and injection amount controls. In the EGR controls, for example, there has been mass-produced a method (for an airflow meter F/B control), in which the airflow to be sucked into a cylinder is feedback-controlled to a target value by measuring it with an airflow meter disposed in an intake line, so as to enhance the precision in the EGR ratio.
In a transient state for acceleration or deceleration, however, the actual airflow into the cylinder and the airflow measured by the airflow meter are different so that the so-called xe2x80x9cmodel-based controlxe2x80x9d has been investigated in various manners considering the transmission delay of air. In this model-based control, the air to flow in the transient state into the cylinder is estimated by calculating a transmission delay in the air physically or in a transmission function on the basis of the airflow signal measured by the airflow meter.
However, the EGR amount recirculated from the EGR passage is highly varied with the back pressure on the EGR upstream side (i.e., on the exit side of the cylinder). Especially in the turbo engine, the back pressure changes highly transiently so that the EGR amount changes to cause an error in the EGR ratio. Especially in the variable turbo engine, the back pressure change is so seriously high that the EGR ratio cannot be precisely controlled by the airflow meter F/B control of the prior art or by the model-based control on the former thereby to fail to prevent the adverse effects such as the smoke emission.
In the case of the Diesel engine for the injection amount control, moreover, the injection amount is made different from a command value by the manufacture tolerance or aging of a fuel injection device so that the fuel becomes excessive or short to cause problems of the smoke emission or the torque shortage. In order to solve these problems, there has been investigated a method for feedback-controlling a fuel amount with an exhaust O2 concentration by providing the exhaust line with an O2 sensor for detecting the exhaust concentration. With the O2 sensor in the exhaust line, however, a time delay occurs till the exhaust gas reaches the position of the O2 sensor. With the delay in the chemical reaction of the O2 sensor itself, moreover, the actual exhaust O2 concentration and the exhaust O2 concentration detected by the O2 sensor have been different to cause a problem that the control precision especially at the transient time drastically drops.
It is an object of the present invention to provide an internal combustion engine control system that is capable of estimating an exhaust O2 concentration precisely.
It is another object of the present invention to provide an internal combustion engine control system that is capable of performing an adequate EGR control and an injection amount control.
The present invention has been conceived on the basis of the background thus far described and has an object to realize an EGR control and an injection amount control, which are excellent in responsibility and highly precise.
According to the present invention, the exhaust O2 concentration of each combustion in a cylinder is estimated by using an intake airflow signal outputted from the intake measuring means, an intake pressure signal outputted from the intake pressure sensor, and command injection amount information calculated by the command injection amount calculating means, and at least one of an EGR valve and the fuel injection amount is controlled in accordance with the estimated exhaust O2 concentration.
By using the intake pressure signal, according to this construction, the total amount of air to enter the cylinder can be detected, and the fresh airflow (i.e., the airflow containing no EGR gas) of the intake passage can be highly precisely detected with the intake airflow signal and the intake pressure signal. From the total amount of air and the amount of fresh air into the intake passage, it is possible to determine the amount of EGR gas into the intake passage. By adding the command injection amount information, moreover, it is possible to estimate the exhaust O2 concentration after each injection highly precisely. According to this method, the exhaust O2 concentration can be estimated before it is actually detected by the sensor, so that the method can control in high responsibility when used for the injection amount control or the EGR control.
The exhaust O2 concentration estimating means may include consumed O2 amount calculating means for calculating the O2 amount to be consumed in terms with the command injection amount.
In this case, the exhaust O2 concentration after injection can be calculated highly precisely by calculating the O2 amount to be consumed with the command injection amount.
The exhaust O2 concentration estimating means may calculate the O2 amount in the gas (containing an EGR gas) to flow into the cylinder, by using the O2 amount in the fresh air sucked into the intake passage and the O2 amount in the EGR gas.
As a result, the O2 amount to flow into the cylinder can be calculated highly precisely to improve the estimating precision of the exhaust O2 concentration.
The exhaust O2 concentration estimating means may calculate the O2 amount in the EGR gas by using the estimated value of the past exhaust O2 concentration calculated beforehand.
In this case, the detection delay is less influenced than the case in which the O2 concentration of the exhaust gas is actually detected by the sensor, so that the exhaust O2 concentration can be estimated highly precisely.
The control system may further comprise: an O2 sensor disposed in an exhaust passage for detecting the actual exhaust O2 concentration; and learning means for controlling the estimated value of the exhaust O2 concentration so that the estimated value may coincide with the output value of the O2 sensor.
As a result, the error of the exhaust O2 concentration estimating means can be reduced to improve the estimating precision of the exhaust O2 concentration.
The control system may further comprise: an O2 sensor disposed in an exhaust passage for detecting the actual exhaust O2 concentration; filtering means for correcting a time delay till the exhaust O2 concentration of the exhaust gas discharged from the cylinder is detected by the O2 sensor; and learning means for calculating a learning correction so that the estimated value of the exhaust O2 concentration may coincide with the output value of the O2 sensor, after filtered by the filtering means, to correct the estimated value of the exhaust O2 concentration with the learning correction.
By executing the filtering, according to this construction, it is possible to detect the difference between the estimated value of the exhaust O2 concentration and the actually measured value (or the output value of the O2 sensor) highly precisely. As a result, the highly precise learning control can also be realized even at the transient time.
The updating of the learning correction may be inhibited under the condition in which the changing rate of the estimated exhaust O2 concentration is no less than a predetermined value.
Generally, the learning is done at a steady time, but the driving state for the steady time is limited in the ordinary drive so that the steady state is difficult especially in the region of a low speed and a high load. In the case of a learning to the transient time, therefore, it is important how far the learning should be allowed.
The error occurs in the filtering when the signal of the exhaust O2 concentration abruptly changes. Under the condition in which the changing rate of the estimated exhaust O2 concentration is no less than a predetermined value, therefore, the filtering precision cannot be warranted so that the learning in the transient state within a predetermined range can be realized by inhibiting the updating of the learning correction.
Here, the estimated exhaust O2 concentration, as termed herein, may be either the exhaust O2 concentration of the exhaust gas to be discharged from the cylinder or the exhaust O2 concentration after filtered.
The dead time and the time constant till the exhaust gas discharged from the cylinder reaches the O2 sensor may be detected from the output value of the O2 sensor when the injection amount in a steady state is finely changed.
The dead time and the time constant or the elements of the filtering are adjusted in advance for every driving conditions of the internal combustion engine but can desirably be corrected during the drive because of dispersions in the internal combustion engine and the O2 sensor. According to the present invention, on the contrary, the exhaust O2 concentration can be finely changed to detect how late the O2 sensor exhibits the reaction, by changing the injection amount finely in the steady state so that the filtering precision can be improved. As a result, a highly precise learning can be done at the transient time.
The exhaust passage may be provided with a catalyst, and the O2 sensor may be disposed on the downstream side of the catalyst.
In recent years, it has been increased to mount a catalytic and post-treating system such as a NOx catalyst or a Diesel particulate filter. The O2 sensor is subject to the influences of the pressure. In case these post-treating systems are mounted, therefore, the catalyst or the like acts a pressure loss member so that the pressure in the vicinity of the sensor rises to cause a problem that the detection precision of the O2 sensor drops.
According to the present invention, on the contrary, by using the filtering to estimate the exhaust O2 concentration highly precisely every moment thereby to correct the delay, the output value of the O2 sensor can be used highly precisely for the learning correction even if the O2 sensor is arranged on the downstream side of the catalyst.
The updating of the learning correction may be inhibited when an addition of the fuel to an exhaust pipe or a post injection for the catalytic control is done.
For the catalytic control, there has been a technique such as the fuel exhaust pipe addition, in which the fuel is added to the exhaust pipe for a predetermined period, or the post injection in which the fuel is injected into the cylinder after the end of a combustion.
However, these fuel components may lead to a reduction in the detecting precision of the O2 sensor. As the chemical reaction in the catalyst is activated by the fuel addition, moreover, the catalyst temperature rises so that soot is burned in the catalyst. Then, the exhaust O2 concentration in the vicinity of the O2 sensor becomes different from that of the exhaust gas when discharged from the cylinder. This difference makes it difficult to retain the precision of the learning control. With these catalytic controls, therefore, the erroneous learning can be prevented by inhibiting the updating the learning correction.
When the absolute value of the learning correction is no less than a predetermined value, the O2 sensor may be decided to be malfunctioning.
The sensor element has to be held at a temperature as high as 600 to 800xc2x0 C. for retaining the detection precision of the O2 sensor. Moreover, there may occur a trouble that the sensor element is cracked with water. In these cases, there arises a problem that a mistaken value is learned. When the absolute value of the learning correction is no less than the predetermined value, therefore, the O2 sensor is decided to be malfunctioning. When the malfunction of the O2 sensor is decided, the learning correction by the learning means may be inhibited.
The estimated exhaust O2 concentration is warranted to have a precision of a certain extent although it contains a model error. Even if the learning correction is inhibited because the O2 sensor malfunctions, therefore, the control can be realized with the model estimating value, so that the EGR control or the injection amount control using the exhaust O2 concentration can be prevented from being seriously influenced.
The control system may further comprise means having a target value of the exhaust O2 concentration for each driving region of the internal combustion engine for feedback-controlling the EGR valve so that the estimated value of the exhaust O2 concentration may coincide with the target value. As a result, the exhaust O2 concentration can be made to follow the target value highly responsively thereby to improve the emission.
The command injection amount may be corrected by re-calculating the injection amount so that the estimated value of the exhaust O2 concentration at the calculating time using the command injection amount may coincide with a predetermined target value. As a result, the exhaust O2 concentration can be controlled for every injections so that the controllability of the exhaust O2 concentration can be improved to improve the emission.
The command injection amount may be set with an upper limit so that the estimated value of the exhaust O2 concentration at the calculating time using the command injection amount may not exceed a predetermined limit value on the rich side. As a result, the smoke can be prevented in advance from being produced, while suppressing the correction of the injection amount to the minimum.
The limit value on the rich side may be given as a function of at least a rotation speed of the internal combustion engine. As a result, in case a torque is needed even in a low rotation speed, the correction of the injection amount can be reduced to improve the acceleration.